1. Field of the Invention
The present invention relates generally to an electric motor assembly. More specifically, the present invention concerns an electric motor assembly that is particularly useful in actuating a valve body within a pressurized working fluid conduit, with the motor assembly including an isolation housing in which the rotor is located, with the housing serving to fluidly isolate the stator from the rotor and from any contact with the working fluid.
2. Discussion of the Prior Art
Those of ordinary skill in the art will appreciate that an electric motor, such as a linear stepper motor, can be used for many different applications, one of which involves shifting a valve body of a valve assembly to control the flow of a working fluid within a system. It is common to use such a stepper motor controlled valve assembly to control the flow of a refrigerant with a cooling system, and examples of such cooling systems are disclosed in U.S. Pat. No. 6,076,368 (“the '368 patent”) and U.S. Pat. No. 6,272,870 (“the '870 patent”).
When such a motor controlled valve system has been used in the past, a conventional linear stepper motor has been enclosed inside of a welded housing in order to seal the coolant inside the system and prevent it from leaking out to the environment. Traditionally, such a welded housing has included a steel container bowl brazed to a threaded brass connector for associating the motor control with the valve assembly. In addition, once a conventional motor is placed within the steel housing, a top cover has been welded onto the steel housing and wiring terminals, such as glass beads, have been incorporated into the cover so that wiring leads can be connected to power and control sources. In such a prior art assembly, the entire motor assembly is disposed within the coolant environment and all of the components are therefore exposed to the working fluid.
While such conventional systems have been satisfactory in some respects, those of ordinary skill in the art will also appreciate that such a complex housing arrangement has resulted in an expensive construction with poor reliability, as the multitude of connections, including glass beads and welds, often become leak points for the pressurized refrigerant. The disadvantages of multiple leak points are typically exacerbated by the fact that many of these assemblies are used in systems that experience high vibration, such as a cooling assembly on a refrigerated truck. Moreover, because the entire motor has been placed within the welded housing, a small motor has been required in order to maintain an acceptable overall footprint, a design constraint that has limited the available motor power for evolving applications.
As refrigerants or other working fluids are improved, or as new substances are mandated by law, the operating pressure of the fluid in newer systems is often significantly higher than in previous iterations of such systems. For example, the new refrigerant R-410-A requires an operating pressure that is between about 50% and 70% higher than that of the previous refrigerant R-22. Such an increase in the operating pressure of a conventional system increases the likelihood of the working fluid leaking out to the environment, and will require more powerful motors than can currently be incorporated into the footprint provided by the welded housing.
The prior art simply does not include an electric motor assembly for use in a valve assembly that will satisfactorily seal the pressurized working fluid within the system and that can provide sufficient power as operating pressures increase.